The field of evolutionary biology has long been interested in the molecular basis of morphological evolution; however a clear understanding remains elusive. Abdominal pigmentation in the subgroup Drosophilinae is a well studied trait suitable for studies to identify the genetic changes culminating in the emergence of similar and diverse pigmentation patterns. In addition to diverse pigmentation patterns it is apparent, based on phylogeny, that similar patterns of pigmentation have appeared independently. In the melanogaster species group sexually dimorphic, segment specific pigmentation has recently evolved. The terminal abdominal segments of males are dark, whereas all segments are lightly pigmented in females. Closely related groups of species are monomorphic, i.e. all segments are lightly pigmented in both sexes. In all species, pigmentation is prevented where the gene products of bric-a-brac (bab), a repressor of pigmentation, are expressed. In dimorphic species, a newly evolved circuitry involving homeotic and sex-determination inputs represses bab expression in the terminal segments of the male, but not the female. This proposal will analyze how Drosophila melanogaster bab gene regulatory elements has evolved to integrate responsiveness to homeotic and sex-determination inputs and the extent that both similar and diverse abdominal pigmentation patterns have evolved through the modification of orthologous bab sequences. Insight from the mechanisms of enhancer evolution and function in Drosophilinae will very likely apply to the understanding of cis-regulatory elements in vertebrates as similar sequence alterations have significant medical implications in humans. [unreadable] [unreadable]